# CSS

Rsbuild provides out-of-the-box support for CSS, including PostCSS, CSS Modules, CSS preprocessors, CSS inlining, and CSS compression.

Rsbuild also provides several configurations to customize CSS file processing.

## Lightning CSS

:::tip
[Lightning CSS](https://lightningcss.dev) is a high-performance CSS parser, transformer and minifier written in Rust. It supports parsing and transforming many modern CSS features into syntax supported by target browsers, and delivers better compression ratios.
:::

Rsbuild uses Rspack's built-in [lightningcss-loader](https://rspack.rs/guide/features/builtin-lightningcss-loader) to transform CSS code. It automatically reads the project's [browserslist](/guide/advanced/browserslist) config and converts CSS code to syntax supported by target browsers.

### Features

- Lightning CSS automatically adds vendor prefixes like `-webkit-`, `-moz-`, `-ms-`, etc., so you don't need to manually add prefixes or use the [autoprefixer](https://github.com/postcss/autoprefixer) plugin.
- Lightning CSS automatically downgrades CSS syntax, allowing you to use modern CSS features such as CSS nesting and custom media queries without worrying about browser compatibility.
- Use [tools.lightningcssLoader](/config/tools/lightningcss-loader) to customize `lightningcss-loader` options.

### Disabling Lightning CSS

If Lightning CSS does not meet your needs, you can disable Lightning CSS and use [PostCSS](#using-postcss) to transform your CSS code.

Steps:

1. Set [tools.lightningcssLoader](/config/tools/lightningcss-loader) to `false` to disable the Lightning CSS loader.
2. Use [@rsbuild/plugin-css-minimizer](https://github.com/rspack-contrib/rsbuild-plugin-css-minimizer) to switch the CSS minifier from Lightning CSS to cssnano or another CSS minifier.

```ts title="rsbuild.config.ts"
import { pluginCssMinimizer } from '@rsbuild/plugin-css-minimizer';

export default {
  plugins: [pluginCssMinimizer()],
  tools: {
    lightningcssLoader: false,
  },
};
```

3. Refer to [PostCSS](#postcss) to configure the PostCSS plugins you need. Here are some commonly used PostCSS plugins:

- [autoprefixer](https://github.com/postcss/autoprefixer): Adds vendor prefixes.
- [postcss-preset-env](https://github.com/csstools/postcss-plugins/tree/main/plugin-packs/postcss-preset-env): Converts modern CSS into something most browsers can understand.
- [postcss-nesting](https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-nesting): Supports CSS nesting.

## CSS minification

When building for production, Rsbuild enables Rspack's built-in [LightningCssMinimizerRspackPlugin](https://rspack.rs/plugins/rspack/lightning-css-minimizer-rspack-plugin) plugin to minify CSS assets for better transmission efficiency.

- You can disable CSS minification using the [output.minify](/config/output/minify) option or customize the options for `LightningCssMinimizerRspackPlugin`.
- You can use [@rsbuild/plugin-css-minimizer](https://github.com/rspack-contrib/rsbuild-plugin-css-minimizer) to customize the CSS minimizer, switching to [cssnano](https://github.com/cssnano/cssnano) or another CSS minimizer.

## PostCSS

Rsbuild supports transforming CSS code through [PostCSS](https://postcss.org/). You can configure PostCSS in the following ways:

### Configuration file

Rsbuild uses [postcss-load-config](https://github.com/postcss/postcss-load-config) to load the PostCSS configuration file in the root directory of the current project, such as `postcss.config.js`:

```js title="postcss.config.cjs"
module.exports = {
  'postcss-px-to-viewport': {
    viewportWidth: 375,
  },
};
```

`postcss-load-config` supports multiple file formats, including but not limited to the following file names:

- postcss.config.js
- postcss.config.mjs
- postcss.config.cjs
- postcss.config.ts
- ...

### tools.postcss

You can also configure the postcss-loader through Rsbuild's [tools.postcss](/config/tools/postcss) option, which supports modifying the built-in configuration through a function, for example:

```ts title="rsbuild.config.ts"
export default {
  tools: {
    postcss: (opts) => {
      const viewportPlugin = require('postcss-px-to-viewport')({
        viewportWidth: 375,
      });
      opts.postcssOptions.plugins.push(viewportPlugin);
    },
  },
};
```

### Configuration priority

- When you configure both the `postcss.config.js` file and the `tools.postcss` option, both will take effect, and the `tools.postcss` option will take precedence.
- If there is no `postcss.config.js` file in the project and the `tools.postcss` option is not configured, Rsbuild will not register `postcss-loader`.

## CSS Modules

Rsbuild supports CSS Modules by default, please read the [CSS Modules](/guide/styling/css-modules) chapter for the complete usage of CSS Modules.

## CSS preprocessors

Rsbuild supports popular CSS preprocessors through plugins, including Sass, Less and Stylus. See how to use them:

- [Sass Plugin](/plugins/list/plugin-sass)
- [Less Plugin](/plugins/list/plugin-less)
- [Stylus Plugin](/plugins/list/plugin-stylus)

## CSS-in-JS

See [CSS-in-JS](/guide/styling/css-in-js) to learn how to use common CSS-in-JS libraries in Rsbuild.

## Inline CSS files

By default, Rsbuild will extract CSS into a separate `.css` file and output it to the dist directory.

To inline styles into your JS file, set [output.injectStyles](/config/output/inject-styles) to true to disable CSS extraction logic. When the JS file is requested by the browser, JS dynamically inserts the `<style>` tag into the Html to load the CSS styles.

```ts
export default {
  output: {
    injectStyles: true,
  },
};
```

This will increase the size of your JS Bundle, so it is usually not recommended to disable the CSS extraction.

## Import from node_modules

Rsbuild supports importing CSS files from `node_modules`.

- Import in a JS file:

```ts title="src/index.js"
/* reference normalize.css */
/* https://github.com/necolas/normalize.css */
import 'normalize.css';
```

- Import in a CSS file:

```css title="src/index.css"
@import 'normalize.css';

body {
  /* */
}
```

In Sass and Less files, it is also allowed to add the `~` prefix to resolve style files in `node_modules`. However, this is a **deprecated feature** and it is recommended to remove the `~` prefix from the code.

```scss title="src/index.scss"
@import 'normalize.css';
```

## Query parameters

### inline

Rsbuild supports importing compiled CSS files as strings in JavaScript by using the `?inline` query parameter.

```js
import inlineCss from './style.css?inline';

console.log(inlineCss); // Compiled CSS content
```

Using `import "*.css?inline"` has the following behaviors:

- Get the compiled text content of the CSS file, processed by Lightning CSS, PostCSS and CSS preprocessors
- The content will be inlined into the final JavaScript bundle
- No separate CSS file will be generated

:::tip

- Rsbuild's Sass, Less, and Stylus plugins also support the `?inline` query parameter.
- Rsbuild >= 1.3.0 supports the `?inline` query parameter.

:::

### raw

Rsbuild supports importing raw CSS files as strings in JavaScript by using the `?raw` query parameter.

```ts title="src/index.js"
import rawCss from './style.css?raw';

console.log(rawCss); // Output the raw content of the CSS file
```

Using `import "*.css?raw"` has the following behaviors:

- Get the raw text content of the CSS file, without any preprocessing or compilation
- The content of the CSS file will be inlined into the final JavaScript bundle
- No separate CSS file will be generated

:::tip

- Rsbuild's Sass, Less, and Stylus plugins also support the `?raw` query parameter.
- Rsbuild >= 1.3.0 supports the `?raw` query parameter.

:::
